The US financial watchdog wants to clamp down on some trading practices
US credit rating agencies will face tighter supervision under new rules adopted by the US financial watchdog.
The Securities and Exchange Commission (SEC) said agencies must disclose more information on past ratings to help investors make informed judgements.
The agencies, which give firms ratings to determine how safe an investment they may be, have been criticised for their role in the financial crisis.
The dominant agency firms include Standard & Poor's, Moody's, and Fitch.
'Flash trading' moves
Head of the SEC, Mary Schapiro, said that investors' reliance on agency ratings "did not serve them well over the last several years".
Earlier this year, credit rating agencies admitted errors were made when assessing some of the financial instruments that have been blamed for the credit crunch.
The agencies have been accused of failing to spot the size and risk of the bad US housing debt that was resold around the world, causing multi-billion-pound losses.
They gave high ratings to sub-prime mortgage investment vehicles that later turned out to be incorrect.
The SEC also proposed rules to ban "flash trading" - the process where certain financial institutions gain access to trading information seconds before it is made public.